1. Field of the Invention
The invention relates to a process for winnowing a heavy and a light fraction form a fine-grain mineral mixture under the action of centrifugal force, in which the fine-grain mineral mixture, mixed with a fluid, is charged as a fluidized current of material in the direction of a main axis, as well as to apparatus for carrying out the process.
2. The Prior Art
A continuously working centrifuge for the separation of solid-liquid mixtures is already known (see U.S. Pat. No. 2,822,127) in which several sieve drums are arranged on the arms of a rotor and are rotatable in a planetary manner about the vertical axis of rotation of the rotor. Each sieve drum is at the same time additionally capable of being set in rotation about its own axis, parallel to the axis of rotation of the rotor. The centrifuge further comprises a distributor device for feeding the mixture to the sieve drums, a material discharge device and a drive device for the rotor and the sieve drums. In this centrifuge, due to the relative rotation of the rotor arms and the sieve drums, there results a cyclic variation of the centrifugal force acting upon the treated material in the sieve drum, so that in each case nearest to the rotor rotation axis a short-term lifting of the material away from the sieve drum wall takes place in the region of the sieve drum wall. This pulsation has the effect that the material is moved by the force of gravity along the sieve drum wall to the outlet. However, with such a centrifuge, in which the solids freed from the liquid emerge at the lower end of the sieve drums, a separation of fine-grain mineral mixtures into fractions is not possible.
Furthermore, a similar centrifuge is known (see U.S. Pat. No. 4,199,459) which likewise is intended for the continuous separation of solid-liquid mixtures and which comprises oppositely rotating filter drums with perforated or closed shells arranged in a planetary manner in a vertical rotor, in which drums the material to be centrifuged does not however move over the drum shell, but rather the solids are conducted away by means of worms or channels penetrating the sieve drums. This centrifuge is not suitable either for the separation of fluidised fine-grain mineral mixtures, because it merely only permits a separation of liquid, while the solids are discharged together.
Finaly, an apparatus for obtaining a light fraction and a heavy fraction from a fine-grain mineral mixture is also known see No. DE-C-1133321 in which a slurry containing the mixture is fed axially to a cylindrical vessel. In the cylindrical wall the vessel comprises at least one helical discharge channel for the heavy fraction and contains a propeller with which the charged slurry is set into swirl or rotation. The discharge of the heavy fraction takes place in the upper part of the vessel which is set into rotational and longitudinal oscillations, while the light fraction is drawn off by means of an immersion syphon or the like. Such an apparatus is solely suitable for the preparation of very fine-grained material, is of relatively complicated and thus costly mode of construction, is prone to interruptions of operation and can achieve only small throughputs per machine unit.
It was therefore the problem of the present invention to produce a process and a cost-favourable apparatus for the separation, especially the continuous separation, of a fine-grain mineral mixture into a heavy fraction and a light fraction, guaranteeing a qualitatively satisfactory, reliable and trouble-free separation of any desired fine-grain mineral mixtures, free of any restrictive conditions as regards the composition by weight, and with a higher throughput.